It is known that a regenerative hybrid vehicle can achieve significant reduction in fuel consumption (hence CO2 reduction) by recovering some of the kinetic energy of the vehicle during deceleration or braking of the vehicle and transforming it into another form of energy which can be stored for future use. One example is the electric hybrid vehicle in which the braking energy is transformed into electric energy and stored in an electric battery. Another example is the inertia hybrid vehicle in which the braking energy is transformed into inertial energy and stored in a spinning flywheel. A still further example is the pneumatic hybrid vehicle in which the braking energy is transformed into pneumatic energy and stored in a compressed air tank. The compressed air can be used to power the vehicle, if the engine can be operated in an air motor mode, or to improve the performance of the engine when it is firing, by increasing the intake manifold pressure in a manner analogous to a supercharger. In the latter case, the compressed air can also be used to compensate for turbo lag if the engine is turbocharged.
The Applicants' earlier EP Patent 1 747 351 discloses a method of operating an internal combustion engine having an engine cylinder with a reciprocating piston, first and second intake ports for admitting gas from an ambient air supply into the engine cylinder, first and second intake valves each arranged between a respective one of the intake ports and the engine cylinder, a non-return valve arranged in the second of the intake ports at a distance from the second intake valve and oriented to allow gas to flow only towards the engine cylinder, and a variable valve actuating system for controlling the opening and closing of at least the second intake valve. The engine has an operating mode in which the second intake valve is opened and closed while the cylinder is fully isolated from the ambient air, to permit gas transfer between the cylinder and an auxiliary chamber temporarily defined by the part of the second intake port lying between the second intake valve and the non-return valve. When the second intake valve is opened, the pressure in the auxiliary chamber is greater than the pressure of the ambient air supply such that no gas escapes past the non-return valve.
The above patent, which is believed to constitute the closest prior art to the present invention, requires the presence of two intake ports and, more significantly, a variable valve actuating system, both of which introduce complexities and add to manufacturing cost.